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Thursday, February 12, 2015

Changing bodies changes minds.

A fascinating review by Maister et al. notes studies showing that inducing illusory ownership over the body of a different race, age, or gender person changes implicit social biases, indicating that multisensory experience of our bodies underpins higher-level social attitudes. I pass on their summaries:

•Multisensory correlations can induce illusory ownership of another person's body.
•Ownership can thus be induced over a body of a different race, age, or gender.
•Incorporating a body belonging to a social outgroup changes implicit social biases.
•The multisensory experience of the body underpins higher-level social attitudes.

Research on stereotypes demonstrates how existing prejudice affects the way we process outgroups. Recent studies have considered whether it is possible to change our implicit social bias by experimentally changing the relationship between the self and outgroups. In a number of experimental studies, participants have been exposed to bodily illusions that induced ownership over a body different to their own with respect to gender, age, or race. Ownership of an outgroup body has been found to be associated with a significant reduction in implicit biases against that outgroup. We propose that these changes occur via a process of self association that first takes place in the physical, bodily domain as an increase in perceived physical similarity between self and outgroup member. This self association then extends to the conceptual domain, leading to a generalization of positive self-like associations to the outgroup.

And here is their description of manipulations of body ownership:

Rubber Hand Illusion (RHI)

Watching a rubber hand being stroked synchronously with one's own unseen hand causes the rubber hand to be attributed to one's own body, to ‘feel like it's my hand’. This synchronous stimulation not only elicits a subjective experience of ownership over the hand, but also causes the perceived location of one's own hand to drift towards the rubber hand and a stress-evoked skin conductance response to be elicited when the rubber hand is threatened. The illusion of ownership over the rubber hand does not occur when the rubber hand is stroked asynchronously with respect to the subject's own hand, and thus experiments investigating body ownership commonly use asynchronous stimulation as a control condition. An illusion of the same intensity can be also developed over a virtual hand by either synchronous visuotactile or visuomotor correlations. This illusion persists through radical transformations such as extensive elongation of the arm or change in the virtual hand position with respect to the real one.

Enfacement Illusion

The enfacement illusion is a facial analogue of the rubber hand illusion. Participants watch a video showing the face of an unfamiliar other being stroked with a cotton bud on the cheek, while the participant receives identical stroking on their own, congruent cheek in synchrony with the touch they see. As in the RHI, synchronous, but not asynchronous, visuotactile stimulation elicits illusory feelings of ownership over the other's face. Enfacement also influences social cognition and produces a measurable bias in self-face recognition, whereby participants perceive the other's face as looking more like their own.

Full Body Illusions

Illusory ownership over a physical manikin body that substituted the participant's real body was demonstrated in. Live video, from cameras attached to the manikin, was streamed to head-mounted displays on the participants, so that when looking down they would see the manikin body visually substituting their own. Synchronous tapping on the manikin body and the real body led to illusory body ownership, in a similar way to the more traditional rubber hand and enfacement illusions. More advanced systems have now been developed, using Immersive Virtual Reality (IVR). Participants wear a head-tracked stereo head-mounted display which provides computer generated images immersing the participant in a virtual world. The participant's own body is substituted by a virtual body, viewed from a first-person perspective, with a motion capture system so that their virtual body moves with their real body movements. This set up results in sensorimotor correlations (visual, proprioceptive, tactile, and motor) that elicit illusions of ownership and agency over the virtual body.